51681721 has 27 divisors (see below), whose sum is σ = 65934351. Its totient is φ = 40373424.

The previous prime is 51681719. The next prime is 51681739. The reversal of 51681721 is 12718615.

The square root of 51681721 is 7189.

It is a perfect power (a square), and thus also a powerful number.

51681721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 7645225 + 44036496 = 2765^2 + 6636^2 .

It is not a de Polignac number, because 51681721 - 2¹ = 51681719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (51681221) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 654160 + ... + 654238.

It is an arithmetic number, because the mean of its divisors is an integer number (2442013).

Almost surely, 2^51681721 is an apocalyptic number.

51681721 is the 7189-th square number.

51681721 is the 3595-th centered octagonal number.

It is an amenable number.

51681721 is a deficient number, since it is larger than the sum of its proper divisors (14252630).

51681721 is an equidigital number, since it uses as much as digits as its factorization.

51681721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 198 (or 99 counting only the distinct ones).

The product of its digits is 3360, while the sum is 31.

The cubic root of 51681721 is about 372.4880310855.

It can be divided in two parts, 5168 and 1721, that added together give a square (6889 = 83²).

The spelling of 51681721 in words is "fifty-one million, six hundred eighty-one thousand, seven hundred twenty-one".